Alkaline reactivation of alumina supported palladium catalysts

ABSTRACT

A PROCESS IS DISCLOSED FOR REACTIVATING ALUMINA SUPPORTED HYDROGENATION BY TREATING THE CATALYST WITH EITHER AN ALKALI METAL HYDROXIDE OR ALKALINE EARTH METAL HYDROXIDE IN DILUTE AQUEOUS SOLUTION TO THORROUGHLY WET THE CATALYST THEN HEATING THE TREATED CATALYST TO A TEMPERAURE OF BETWEEN ABOUT 100*C. AND ABOUT 500*C., AND ALLOWING THE CATALYST TO COOL.

United States Patent ALKALINE REACTIVATION 0F ALUMINA I [,[SUPPORTED PALLADIUM CATALYSTS James E. .Williams and Jean 'C Fleischer, Kingsport, Tenn 'assigno'rs to Eastman Kodak Company, Rocheser .Y. NdDx-awiug. Filed Mar. 30, 1972, Ser. No. 239,783

Int. Cl. Blllj 11/18 US. Cl. 252-412 Claims ,T his inventionirelates to a method of reactivating spent alumina-supported palladium hydrogenation catalysts. ETIii' mesa catalytic hydrogenation processes in which organic materials are hydrogenated and in which metallic palladium catalysts are employed, the activity of the cata- =lysft declines With.continued use. In the hydrogenation of il'nsatur'ated aliphatic andaromatic organic esters, for example, a metallicpalladium on alumina catalyst is com- "nionly used. This is a relatively expensive catalyst, and slowly loses activity with. continued use. A more desirable alternative to catalyst replacementis its. regeneration to a condition which would be acceptable for-further use. The regenerated catalyst should preferably be as active and selective? to the desiredproduct as a new catalyst.

It is well known in the art to use steam or hot gases to volatilize organic liquids and thus remove them from the catalysts, -It is also known to. subject spent or fouled cataly sts to an oxidizing treatment to reactivate the catalyst. An object of the present invention is to provide an effective and improved method for reactiva-ting spent hydrogenalion catalysts comprisingmetallic palladium supported on alumina; A specific object is to provide a method for reactivating and improving selectivity of spent hydrogenation catalysts comprising spentpalladium on alumina, which catalysts have become inactivated, or partially inactivated, through use in catalyzing the hydrogenation of organic esters. These and other objects will be apparent from the following description of the invention.

,Although theginvention is described herein broadly as being applicable to catalysts used in the hydrogenation of iln'satura'ted aliphatic and aromatic esters, it is particularly applicable to catalysts usedin the hydrogenation of such esters containing from about 3 to about carbon atoms, such as? .dimethyl terephthalate, dimethyl isophthalate,

bnometfiyl eleare. nd d ma h m r i The above objects are accomplished in accordance with it ijs inyefrition by f'a process which comprises treating the hydrogenation catalyst of metallic palladium supported on alumina with an aqueous solution of an alkyli metal hydroxide or alkaline earth metalhydroxide and subsequently'heating the catalyst, I I

The process is preferably practiced by first draining the spent, or at least partially inactivated, palladium on aluminacatalyst' of excess li'quidrs'ulting from the hydrogenation process of--unsaturated aliphatic or aromatic esters The catalyst may then be washed with a volatile organic solvent such as acetone, methanol or ethyl ace handled. Although the washing step is preferred, it is not gesspmial to lth process accordingto this invention. Any

3,824,193 Patented July 16, 1974 are then removed by steaming or by stripping with hot nitrogen at a temperature above the boiling point of the solvent. The catalyst is then contacted with a dilute aqueous solution of an alkali metal hydroxide or alkaline earth metal hydroxide, thereby saturating or wetting the catalyst fully with the alkaline solution. As soon as thorough wetting is accomplished, excess solution is removed and the catalyst is heated in air, or a mixture of air and inert gas. Care should be taken. during heating to avoid overheating which may cause loss of activity of the catalyst. The heating temperature may be within the range of from about 100 C. to about 500 C., preferably between about 200 C. and about 450 C. for a time sufficient to thoroughly dry the catalyst. The catalyst is subsequently cooled, or allowed to cool, and is then ready for reuse as a hydrogenation catalyst.

The caustic solution used to treat the catalyst in accordance with this invention is prepared by mixing the alkali metal hydroxide or alkaline earth metal hydroxide with water. The temperature of the solution while it is being used to treat the catalyst is not critical, and approximately room temperature and atmospheric pressure are perfectly suitable. The catalyst is treated, or brought into contact with the alkaline solution by dipping the catalyst in the aqueous alkaline solution, spraying the catalyst with the solution, pouring the solution into an container with the catalyst, or any other manner known to one skilled in the art. It is preferred that promptly after attaining a thorough wetting of the catalyst by the alkaline solution, the heating step be started to prevent the possibility of undesirable attack on the alumina by the alkaline solution. During heating, an exothermic reaction occurs. Following the reaction, the catalyst is cooled by suitable cooling means, or allowed to cool to about room temperature and it is ready for reuse in a hydrogenation reaction.

Suitable alkali metal hydroxides and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, barium hydroxide, and calcium hydroxide. Preferably, the alkaline material is used in concentrations of from about 0.1 to about 10 Weight percent and most desirably from about 0.5 to about 5 weight percent of the solution.

The term inactivated or spent catalyst is used herein to mean a catalyst comprising metallic palladium supported on alumina, whose activity has been either completely or partially destroyed through use in catalyzing the hydrogenation on unsaturated aliphatic or aromatic ester. The term reactivation is used to mean the restoration, either partially or completely, of the effectiveness of such a spent catalyst to catalyze such hydrogenation reactions.

Surprisingly, it has been found that the elfectiveness of new palladium on alumina catalyst is increased by use of the method according to the invention. When new catalyst is used, it is of course understood that draining, cleaning, etc., is unnecessary.

. The procedure for determining the activity and selectivity of the catalyst will now be described. A one-liter autoclave is charged with 230 g. of unsaturated ester as called for in the examples. An 8.0 g. sample of palladium supported on alumina catalyst is suspended in a basket made of stainless steel screen by means of a support attached to the head of the autoclave, at a height such that the catalyst would normally be above the liquid level of the ture, the stirrer speed is increased so that the vortex created volatile-organic-materials which remainon" the catalyst would cause the liquid ester to impinge on the catalyst basket and therefore would contact the catalyst. Pressure inside the autoclave is brought to 2000 p.s.i.g. by the addition of hydrogen. After 2 hours, agitation with the stirrer is stopped, the reactor is cooled and dismantled. The product is removed, weighed and analyzed. Quantities by weight of unsaturated ester and hydrogenated material are determined by quantitative gas chromotography. The column used is 10 weight percent Carbowax 20M, a polyethylene glycol sold by Union Carbide, on Gas- Chrom Z, a packing support sold by Applied Science Laboratories, Inc. The column is 10 feet long and %-in. outside diameter tubing, and is operated at 174 C. Acid by-product is determined by titration with dilute base. Conversion of unsaturated ester to hydrogenated material and to acid, and yield of hydrogenated material are calculated as follows:

(a) Conversion of unsaturated ester to hydrogenated material: (moles hydrogenated material produced+ moles unsaturated ester in feed) X100 (b) Conversion of unsaturated ester to acid'=(moles acid produced-e-moles unsaturated ester in feed) X100 Yield=(moles hydrogenated material produced+ moles unsaturated ester consumed) 100 The following examples are submitted for a better EXAMPLE v1 A 300 gram portion of steamedanddried catalyst is impregnated with a solution of 3.0 grams sodium hydroxide in 110 milliliters water. The"'catalyst is' then dr'ied, and subsequently charged to theVycortube of Example V and heated in an air-nitrogen mixture'as in Example V. Results of activity tests'on' samplesof the regenerated catalyst are shown in Table'I, Example VI, runs a' f.

TABLE 1 Percent understanding of the invention.

EXAMPLE I Run M3 121 gm 0! Ex. No. Catalyst description Acid DMCD (DMCD Samples of unused 0.5% palladium on alumina catalyst v p from a typical lot are tested by the above procedure in (a) gg gg g l i t the hydrogenation of dimethyl terephthalate (DMT) to (b) 2.8 "73.2 .;93.i dimethyl 1,4-cyclohexanedicarboxylate (DMCD). The 33% I 82:8 results are shown in Table I, Example I, runs af. 3 7 gig EXAMPLE 11 11--.- (a) Used all adlm i 01181112115118 2.s;- 42 mv 54.5 08 a YS 3C9 one-was e (b) .-....d0 2.8. 46.9 85.6 Samples of .Panadmm on alunlma catalyst are III... (a) Used palladium on alumina 5.5 69.2 '87.? partially deactivated through use in the hydrogenatlon of catalyst, steanted, and DMT to DMCD are obtained. A 175 g. portion of the (b) g at 350 4 3 703 902 catalyst is washed five times with 100 milliliter portions (0) 415 as: 0 3914 of acetone to remove visible organic deposits. The samples ((1) (8) 4.3 67.5 89.8 are then dralned and timed under mtrogen at room tem (t) 4.2 66.8 90.1 perature. The results of activity tests are shown 1n Wu" (8) Used palladium on alumina 4 m8 9: Table I, Example II, runs a and 1.). catalyst, steamed, NaOH- gggatgd, calcined at i EXAMPLE III 93 c a 2. 5 74. 7 95. a A 500 8. quantity of spent palladium on alumina catai 82- lyst is steamed for 4 hours with saturated steam at atmos- U d 11 di lumi 5.8 74.4 88.8 pher c pressure and drled for approxlmately 12 hours at (a) zg lf s g g f I I y v 150 C. A 100 g. quantity of this catalyst is heated for heated with air and 24 hours at 350 C. in a furnace. Samples are cooled (b) nit r agen to about 350 0. 757 5 and tested by the above procedure in the hydrogenation (c) a 5:0 75: 3 8911 of DMT to DMCD. The results are shown in Table I, 8 2-2 Y 33-? J 23; Example III, runs a-f. r 418 66:7 3915 v1.... Us a alladlumo lumi a, 2.5 74.3 95.0 EXAMPLE IV (a) c ta lyst, steame r lj NaOiltgeateggirfild heatted ilzgitht aran rogen oaou A 100 g. portion of the steamed and dried catalyst of (b) 3 0 9 Example III is impregnated with a solution of 1.0 g. of (c) x 1 1 Q 1 sodium hydroxide dissolved in 35 milliliters water. 23 gg-g'j .gg-g Promptly after mixing the catalyst in the solution to (9 a1 53:3. 921.7 accomplish thorough wetting, it is heated to remove excess water. Samples of the dried catalyst are calcined in a furnace at 350 C. for 24 hours, then cooled and EXAMIfLE VII tested as above. The results are shown in Table I, Ex- Example I is repeated using new palladium on alumina ample IV, runs a-f. I catalyst for hydrogenation reaction as follows:

Percent I Cgmilersiion fh Yeld o y r0- 0 y to- Temp., genated' w enated Unsaturated ester Hydrogenated material 0. material r aterial a Monomethyl maleate..- Monomethyl succinate ca, 175 ca. 70,: ca. 90-94 h... Dimethylmaleate Dimethylsuccinate ca. 96 ca. 96

0.... Dimethylisophthalate. Dimethyl1,Bcyclohexanedicarboxylate... ca. ca 93 EXAMPLE VIII Example II is repeated using acetone-washed used palladium on alumina catalyst for hydrogenation reactions as follows:

6 a mixture of air and inert gas to a temperature of between about 100 C. and about 500 C., to dry the alkaline material in place, and (e) allowing the catalyst to cool.

Percent Conversion Yield to hydroof hydro Temp, genated genated Unsaturated ester Hydrogenated material C. maten'al material a. Monomethyl maleate Monomethyl succinate ca. 175 ca. 40 ca. 70 b-.- Dimetliyl maleate Dimethyl suecinate sca. 75 ca. 50 ca. S2 c Dimethyl isophthalate- Dimethyl, 13-cyclohexaned rb ylate... ca. 250 ca. 42 ca. 85

EXAMPLE IX Example HI is repeated using used palladium on alumina catalyst, steamed and calcined at 350 C. for hydrogenation reaction as follows:

2. A process according to Claim 1 wherein said alkaline material is sodium hydroxide.

3. A process according to Claim 1 wherein said alkaline Percent Conversion Yield to hydrcof hydro- Temp., genated genated Unsaturated ester Hydrogenated material 0. material material a Monomethyl maleate-.. Monomethyl succinate ca. 175 ca. 72 ca. 87 b. Dlrnethyl maleate Dimethyl succinate ca. 75 ca. 93 cav 93 o Dimethyl isophthalate. Dimethyl1,3-cyelohexanedicarbonate... ca. 250 ca. 70 ca. 88

EXAMPLE X material in aqueous solution comprises from about 0.1%

d to about 10% by Weight of the solution.

4. A process according to Claim 1 wherein said alkaline- Percent Conversion Yield 1;o hydrooi hydro Temp, genated genated Unsaturated ester Hydrogenated materiel 0. material material a Monomethyl maleate.-. Monomethyl sueelnate ca. 175 ca. 72 ca. 94 b.-. Dimethylmaleate Dimethylsuccinate ca. 75 ca. 97 ca. 98 e.. Dimethyl isophthalate. Dimethyl1,3-cyclohexanedicarbonate ca. 25 ca. 75 ca. 94

All parts and percentages used herein are by weight unless otherwise specified.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A process for the regeneration of spent palladiumon-alumina catalyst used in the hydrogenation of unsaturated aliphatic and aromatic organic esters which comprises the steps of (a) removing liquids and volatile material which are associated with said catalyst as a result of its use in a hydrogenation process,

(b) steaming the catalyst from step (a),

(c) thoroughly saturating said catalyst with an aqueous solution of an alkaline material selected from the group consisting of alkali metal hydroxides and allcaline earth metal hydroxides in sutficient quantity to thoroughly wet said catalyst,

(d) heating the alkaline treated catalyst in air or in References Cited UNITED STATES PATENTS 3,650,983 3/1972 Miller 252-412 2,925,391 2/1960 Lait et a1. 252-412 3,480,558 11/1969 Lum et al 252-416 3,214,385 10/1965 Kolyer 252-412 3,194,844 7/1965 Silber et a1. 252-412 DANIEL E. WYMAN, Primary Examiner P. E. KONOPKA, Assistant Examiner US. Cl. X.R. 

